Electronic circuit breakers are employed in numerous applications in order to detect a short circuit across a load, "trip" in order to protect the load from electrical damage, and then automatically reset after the load has been disconnected. For example, on various types of assembly lines, such as those used to manufacture automobiles, the electrical system of each vehicle is tested by a worker before the electrical battery is installed in the vehicle. In order to test the vehicle's electrical system, a worker connects an external 13-volt d.c. supply to the vehicle's battery cables. In the event that one or more portions of the vehicle's electrical system contains a short, damage to the external power supply is prevented by a circuit breaker interposed between the vehicle's electrical system and the power supply.
In the past, known mechanical and electronic circuit breakers used in the context described above required manual resetting each time the circuit breaker was tripped by a short circuit. In the case of an assembly line operation where short circuits in newly assembled products occur with relative frequency, it becomes time-consuming and troublesome for the assembly line worker to reset the circuit breaker each time it is tripped. Reset mechanism must be provided which is physically adjacent the assembly line worker, moreover the worker may not always have sufficient time to properly reset the circuit breaker, and in some cases, the worker may inadvertently neglect to operate the reset mechanism. Obviously in a large scale assembly line operation, the line may not be shut down simple to allow a worker additional time to complete his assigned task; as a result, the worker may fail to test some products, in which case electrical defects may go unnoticed by the manufacturer, or the required electrical testing must be performed in a non-assembly line operation after the vehicle is removed from the line.
None of the known prior art circuit breakers provide an acceptable solution to the problem mentioned above. For example, U.S. Pat. No. 3,538,426 to JONES discloses an electronic circuit breaker which interrupts current flow to the load for short periods of time when an over-current defect is detected, and subsequently resumes delivery of electrical power regardless of whether or not the electrical defect is still present. Thus, a circuit breaker of this type continues to switch on and off, and therefore intermittently delivers potentially damaging current through a short circuited system. None of the known prior art circuit breakers provide, however, a system in which current from a power supply is continuously interrupted but is automatically reset when the load is removed therefrom.
Accordingly, it is a primary object of the present invention to provide an electronic circuit breaker which eliminates the deficiencies inherent in prior art circuit breaker designs and is operative to interrupt current flow to a load having a short circuit defect until the load is removed therefrom, but which is automatically reset in response to disconnection of the load therefrom. Thus, the circuit breaker of the present invention is automatically reset merely by disconnecting the load therefrom and is readied for connection to another load without the need for manually operating reset mechanisms or the like.
Another object of the present invention is to provide a solid-state circuit for detecting over-current conditions in an electrical load, without the need for mechanical switches or components.
A further object of the invention is to provide a circuit breaker of the type mentioned above which reduces the current flow from a power supply to a load having a short circuit condition to a relatively low level until the load is removed from the circuit breaker.
A still further object of the invention is to provide a circuit breaker of the type described above which introduces a relatively low voltage drop across the power supply lines even at relatively high current levels.
These and further objects of the invention will become clear or will be made apparent during the course of the following description.